Methods for Creating a Simulated Watercolor-Painted Image from a Source Image

ABSTRACT

A method of creating watercolor images from a source image may include some or all of: scaling down and lightening the source image; converting the lightened image to a single channel grayscale image; blending a noise pattern with the lightened image to add random jitter; overlaying an edge detection map to produce an edge buffered control image; determining a main set of colors in the source image: determining boundaries for each region where the main set of colors appear; coloring in multiple passes using one color at a time, with a diffusion of water technique emulating wet-on-wet watercoloring; coloring each of the main set of colors, by coloring from a light to dark order; enhancing the edges of the regions to model the areas where a watercolor artist would maintain separation; and compositing to add sedimentation texture; flocculation texture; a drawing layer; and a paper texture pattern.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/952,723, filed on Nov. 25, 2015, which claims priority on U.S.Provisional Application Ser. No. 62/084,790, filed on Nov. 26, 2014, thedisclosures of which are incorporated herein by reference. Thisapplication incorporates by reference the disclosures of the Applicant'sU.S. patent application Ser. No. 14/250,475, filed on Apr. 11, 2014, nowissued as U.S. Pat. No. 9,478,004, having the title, “Method and Systemfor Analog/Digital Image Simplification and Stylization.”

FIELD OF THE INVENTION

The present invention relates to a computer-implemented process formodifying a source image, and more particularly to a process forsimulating an artist's redrawing technique for creating a digitalwatercolor image from a source image.

BACKGROUND OF THE INVENTION

The practice of painting images dates back over 30,000 years, as shownby the prehistoric cave paintings discovered in many parts of the world,including Africa, Australia, and Europe (e.g., the Chauvet-Pont-d'ArcCave in the south of France). The Greeks and Romans painted on woodpanels—a practice that continued until the use of canvas becamewidespread, during the Renaissance period, particularly during the early16^(th) century.

Watercolor painting involves the use of semi-transparent pigments ratherthan the mostly opaque acrylic- and oil-based paints, but is consideredto be just as old. However, watercolor painting did not become firmlyestablished as an art medium until the Renaissance. The practice wasprominently used for botanical and wildlife illustrations on woodblock,vellum, and paper. Watercolor paintings were eventually used formapmaking around the time when the practice proliferated during the18^(th) century, which was particularly the result of the works ofseveral English artists. The most notable watercolor painters of thatperiod are perhaps Paul Sandby, who became known as the “father ofEnglish watercolor,” Thomas Girtin, for his landscape paintings, andJoseph William Mallard Turner, who is credited as developing thewatercolor painting technique of painting in stages, and of refining animage through a sequence of washes and glazes. Later artists such asJohn Constable and David Cox are credited as developing the techniquesof wiping and scratching out the colors.

Today's artist uses watercolor paints that are a combination of pigmentsground into small particles to provide the color, a natural gum arabicor synthetic glycol binder that is used to suspend the pigment, butwhich permits it to adhere to the paper, various other additives (e.g.,a surfactant to reduce surface tension of the liquid to permit it tosoak into the paper), and a solvent (i.e., water), which evaporates asthe paint dries.

Today's artist also uses paper that is particularly manufactured forsuch applications, and may be made of wood pulp, at the low end, or fromcotton or linen at the high. The fibers of the paper are porous and veryabsorbent, so the paper is usually lightly treated with sizing (e.g.,cellulose), to slow the absorption of the paint, but which maynonetheless permit the pigment granules to penetrate, depending upon thegrain size. The ability of certain pigment granules to separate from thebinder and settle into valleys within the paper to produce a grainytexture, when dry, is known as granulation. Also, some pigments (e.g.,lapis, lazuli, and ultramarine) exhibit certain electrical propertiesgiving them the tendency to be drawn towards each other to form clumpson the paper, to provide a similar grainy texture or speckling known asflocculation.

Watercolor painting is unlike painting with acrylic or oil based paints,which stay as they are laid, as watercolor paints, conversely, are moreactive, and require knowledge of its behavior. There are two basictechniques for watercolor painting, which are known as wet-on-dry andwet-on-wet painting. With the wet-on-dry technique, the brush appliesthe watercolor paint onto a dry paper, whereas for the wet-on-wettechnique, the paint is applied to a region of paper that had alreadybeen saturated with water or watercolor paint. There are a multitude offurther delineated techniques, many of which are used only with respectto wet-on-wet applications, each of which produce particular effects.Some of these further techniques are known as back-runs, paintdiffusion, pouring color, dropping in color, salt texturing, cling-film,drybrush, edge darkening, etc.

Because of the popularity of the unique effects produced by the variouswatercolor painting techniques, there has been substantial interest inconverting a source image of various different kinds (e.g., an originaloil painting, a digital photograph, etc.), into a watercolor painting.This conversion had been done manually by artists, but with the abilityto digitize an image and manipulate it using a computer system, methodsfor digitally converting source images have also arisen. These methodsexhibit varying levels of success at realistically mimicking painterlyeffects to create a realistic simulated Watercolor image. The presentinvention is directed to a process that converts a source image into asimulated watercolor-painted image to more closely resemble thetechniques and realism achieved when an artist manually creates thepainting using watercolor paints on paper, and which may run efficientlyon different devices and architectures, particularly low-power mobiledevices.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a process for converting asource image into a simulated watercoior-painted image.

It is another object of the invention to provide a process forconverting a source image into a simulated watercolor-painted image thatis created in a similar fashion to the way an artist would manuallypaint the image from scratch using watercolor paints on paper.

It is a further object of the invention to provide a process forconverting a source image into a simulated watercolor-painted image thatcan run efficiently on different devices and architectures, especiallylow-power mobile devices.

Further objects and advantages of the invention will become apparentfrom, the following description and claims, and from the accompanyingdrawings.

SUMMARY OF THE INVENTION

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

The present invention is directed to method steps, a portion of which orall of which may be used to process a source image, to make the imageappear like a watercolor painting.

The image processing pipeline includes a combination of image processingfilters and compositing steps, and includes a unique pigment propagationstage. The pigment propagation stage simulates the spread of pigmentthrough wet paper.

The simulation is empirical it is controlled by numeric parameters andinput images.

The simulation is an approximation, which reduces the process to a setof steps that can run efficiently on different computing devices andarchitectures, particularly low-power mobile devices, and may utilizeboth an edge buffer and a pigment propagation buffer.

The herein disclosed methods for creating a simulated watercolor-paintedimage from a source image may begin by inputting the source image intothe system.

To create an edge buffer, the source image may first be scaled down,because the size of the source image will affect the size of the pigmentpropagation stage.

Next, the scaled-down version of the source image may be gamma adjustedto be lighter. This may done for two reasons: first, empirically,watercolor images are lighter and brighter than photographic images; andsecond, the pigment propagation stage may simulate a subtractive colormodel, in which, as colors bleed and mix, they become darker.

Next, an edge buffer may be created. There are 3 main steps used tocreate the edge buffer. A base image—the scaled-down and lightenedversion of the source image—is first converted to a single-channelgrayscale image. In the second step, a noise pattern is blended with thegray scale image, which adds random jitter that simulates the randomnessof paper fibers, and may be used to affect the subsequent spread ofpigment when running the herein disclosed pigment propagation stage.Finally, a special edge detection map is overlaid onto thejitter-blended grayscale image to create the edge buffer, which is usedto enforce very high barriers that the kernel in the pigment propagationstage will not cross. This simulates the artist's technique of leavingwhite gaps between regions that the artist does not want to blend,because the pigment propagation stage may treat the entire image surfaceas ‘wet’ and potentially blendable, which in watercolor paintings isknown as the wet-on-wet painting technique.

To create the pigment propagation buffer, which may be the same size asthe edge buffer, the scaled down and lightened version of the sourceimage from above may be utilized. An image segmentation algorithm is runon the scaled down and lightened source image, which may operate tocreate regions of similar color. Although the pigment propagation stagecan use any color source for the pigment buffer, the herein disclosedprocess preferably deposits pigments in stages, using the pigmentbuffer, to simulate an artist's painting process. Segmented regions areused to create clusters of colors that will eventually be copied to thepigment buffer over time.

Thereafter, the color regions axe sorted by color value (lightest todarkest), which will become the order by which they will be deposited bythe algorithm into the pigment buffer, and will subsequently be utilizedthereafter, because when painting wet-on-wet, artists will generallystart with the lightest colors and end with the darkest. This preventsdark areas of paint from bleeding for too long, which may ruin lighterareas of the painting that are supposed to remain light.

The edge delineation map from the previous step is also used, to ensurethat no pigment is placed near edges that have been deemed to be cleanlydelineated.

Next, the pigment propagation stage can begin. The pigment propagationstage operates to deposit each of the regions of color that weredetected by the image segmentation algorithm. The pigment propagationstage deposits the colors in multiple passes, depositing only one colorat a time, in each of the passes, using the detected colors and theregion boundaries that were sequentially stored in the pigment buffer.The simulation uses a diffusion of water technique that emulateswet-on-wet watercoloring. So, the pigment propagation, stage operates todeposit the regions of color, with a darkening only color diffusion,with the order of color deposition going from the lightest colors to thedarkest colors (i.e., the color value order of the pigment propagationbuffer), while nonetheless enforcing each of the strict edge boundarieswithin the edge buffer.

The output of pigment propagation stage is then sent through severalcompositing stages, which may add watercolor sedimentation andflocculation textures that may be created by scanning real watercolorsurfaces and/or generated with synthetic noise algorithms, and alphablending them therewith. Additionally, a drawing layer may be compositedtherewith, as well as a paper texture pattern.

In summary, the process may be succinctly described as including some orall of the following steps (note that some steps may optionally beperformed to provide desired effects or results):

-   -   inputting a source image;    -   identifying areas of importance within the source image (e.g.,        faces of people); which areas receive a sharpening pass that        create boundaries of increased contrast, making it difficult for        pigment to cross over in the coloring . . .    -   scaling the source image; i.e., upscaling        (interpolated-information is added) or downscaling (information        is discarded)    -   adjusting the luminance values for lightening of the scaled down        image; e.g., linear (histogram scaling and shifting) and        non-linear adjustments (screen blend with the source and        destination images being the same image), or gamma adjustments .        . .    -   converting the lightened image to a single channel grayscale        image;    -   blending a noise pattern with the grayscale image to add random        jitter to simulate the randomness of paper fibers;    -   overlaying an edge detection map to produce an edge buffered        control image;    -   determining a set of different colors used in the source image;    -   determining boundaries for each region where each of the colors        of the set of colors appear, sorting the color regions according        to color value, and storing the ordered colors and color        boundaries in a pigment buffer;    -   pixel averaging by computing the weighted mean of each neighbor        pixel; which may be for example, as disclosed in “Pixel        Averaging Smooth Graphics Effects,” by David Cook, the        disclosures of which are incorporated herein by reference.    -   coloring one color at a time in multiple passes, using the        ordered set of colors and region boundaries in the pigment        buffer, in a diffusion of water technique emulating wet-on-wet        watercoloring; i.e., simulating the artistic process of layering        (placing wet colors on top of dry colors) by compositing        independent runs, or, simulating the artistic process of placing        wet colors next to dry colors so they don't bleed by using a new        buffer that controls the strength of the herein disclosed        coloring effect (pigment propagation stage) at each pixel, e.g.,        dry pixels are not written to or read from . . .    -   coloring each of the colors of the set of colors, with a        darkening only color diffusion, by coloring from a light to dark        order, using the color order of the pigment buffer;    -   using the edge buffered control image tor each coloring pass to        control the diffusion geometry for the regions but not the        color;    -   adjust the lightness of the colored image for aesthetic reasons;    -   running a convolution filter similar to the unsharp-mask of        application Ser. No. 14/250,475, but which only darkens edge        regions, to simulate the effect of pigment particles traveling        to the edge of wet pools as they are evaporating;    -   compositing to add sedimentation texture;    -   compositing to add flocculation texture;    -   compositing to add a paper texture pattern; and    -   compositing to add a drawing layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

The description of the various example embodiments is explained inconjunction with the appended drawings, in which:

FIG. 1 illustrates a source image being scaled down for use in creatinga simulated watercolor-painted image, after being input into the system.

FIG. 2 illustrates gamma adjusting of the scaled-down source image ofFIG. 1, to produce a lighter version thereof.

FIG. 3 illustrates converting the gamma adjusted, scaled-down version ofthe source image into a single channel grayscale image.

FIG. 4 illustrates the prior art conversion of a single channelgrayscale image, using a bi-lateral filter, into a blurred image.

FIG. 5 illustrates converting of the grayscale image of FIG. 3 into anEdge Buffered Image according to the present invention, using a noisepattern blended with the grayscale image, and using an edge detectionmay that is overlaid onto the blended grayscale image.

FIG. 6 illustrates, the pigment propagation stage of the simulation, inwhich coloring occurs one color at a time, in multiple passes, based onthe pigment buffer, with the edges enforced in accordance with the edgebuffer.

FIG. 7 illustrates compositing of the image resulting from the pigmentpropagation stage of FIG. 6, with sedimentation texture, withflocculation texture, with a drawing layer, and with a paper texturepattern.

FIG. 8 is a schematic illustration showing an exemplary computing unitcapable of being programmed by the instructions of the software of thepresent invention, and which may include personal computers, cellularphones, and other mobile devices.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout this application, the word “may” is used in apermissive sense (i.e., meaning having the potential to), rather thanthe mandatory sense (i.e., meaning must). Similarly, the words“include”, “including”, and “includes” mean including but not limitedto.

The phrases “at least one”, “one or more”, and “and/or” are open-endedexpressions that are both conjunctive and disjunctive in operation. Forexample, each of the expressions “at least one of A, B and C”, “one ormore of A, B, and C”, and “A, B, and/or C” means A alone, B alone, Calone, A and B together, A and C together, B and C together, or A, B andC together.

Furthermore, the described features, advantages, and characteristics ofany particular embodiment disclosed in the following specification, maybe combined in any suitable manner with any of the other embodimentsdisclosed herein.

The present invention is directed to method steps, a portion of which orall of which may be used to process a source image, to make the imageappear like a watercolor painting.

The herein disclosed methods tor creating a simulated watercolor-paintedimage from a source image may begin by inputting the source image intothe system, such as source image 11 shown in FIG. 1, and by Identifyingareas of importance within the source image (e.g., faces of people),which areas may receive a sharpening pass that create boundaries ofincreased contrast, making it difficult for pigment to cross over,during the coloring stage described hereinafter.

The source image 11 may next be “scaled,” which is symbolically shownfor image 13 in FIG. 1 by physically reducing the image size. However,“scaling” of the image herein actually involves either downscaling ofthe image where certain information is discarded, or upscaling of theimage where information is added. Of course, the processing may proceedwithout such sealing of the source image. However, the source image maypreferably be downscaled, because the size of the source image willaffect the size of the pigment propagation stage, because the pigmentpropagation stage works with cells that correspond to the pixels in thesource image. Using more cells in the pigment propagation stage requiresmore computational power.

With downscaling, certain information is discarded—particularly suchinformation that an artist would ignore. For example, most artistspainting a portrait would not paint the pores in the person's face,therefore, the algorithm of the present invention throws out this veryhigh frequency information (i.e., high frequency information that mayexceed a threshold). When such information is retained, it may create anartistic effect that is realistic; conversely, when such information isdiscarded (by down scaling) it may create an artistic effect that ismore “impressionistic.” The image may also be down-scaled so that it mayrun in a reasonable amount of time on whatever platform the algorithmmay be implemented on by the user—which platform may not have muchcomputational power.

Next, the scaled version 13 of the source image 11 may be adjusted to belighter, to be as shown for image 15 in FIG. 2. This lightening maybroadly include doing linear (histogram scaling and shifting) and/ornon-linear adjustments (screen blending with the source and destinationimages being the same image). In an alternate embodiment, the algorithmmay accomplish lightening by gamma adjusting the source image, whichinvolves applying a logarithmic adjustment (i.e., V_(out)=(V_(in))*) tothe luminance values for the image.

This lightening may performed for two reasons: first, empirically,watercolor images are lighter and brighter than photographic images; andsecond, the pigment propagation stage disclosed hereinafter may simulatea subtractive color model, in which, as colors bleed and mix, theybecome darker. Note that with a subtractive color model, a limitednumber of colors—paint pigments—are mixed to create additional colors,each being created by partially or completely subtracting (i.e.,absorbing) some wavelengths of light and not others. For example, theprimary subtractive colors are cyan, magenta, and yellow.

Next, an edge buffer image 21 may be created. There are 3 main stepsused to create the edge buffer image 21. A base image—the scaled-downand lightened image 11 made from the source image 11—is first convertedto a single-channel grayscale image 17, as seen in FIG. 3. In the secondstep, a noise pattern is blended with the grayscale image 17, which addsrandom jitter that simulates the randomness of paper fibers, and may beused to affect the subsequent spread of pigment when running the hereindisclosed pigment propagation stage. The noise can be synthetic (i.e.,generated by computer), or it may instead be derived from digitizingreal textures (e.g., digitizing sandpaper, paper, etc.). A particularnoise pattern may be used to provide a specific effect—evenlydistributed noise creates randomly dispersed pigment, whereas noisepatterns with strong direction gradient (e.g., wood grain) willdistribute pigment in the direction of the “grain.” It is alsoadvantageous to composite various synthetic noise algorithms, such asPerlin noise algorithm and Gaussian noise to create textures that looklike watercolor sedimentation/flocculation effects, where it isdifficult to obtain these effects from scans of real watercolorsurfaces. Creating the textures synthetically also allows for much moreprecise control in achieving the desired effect than using real paintbecause all the factors in real watercolor painting can't be preciselycontrolled (paper density, ambient humidity, etc.).

Finally, a special edge detection map 19 is overlaid onto thejitter-blended grayscale image to create the edge buffer image 21, whichmay be used to enforce very high barriers that the kernel in the pigmentpropagation stage will not cross. This simulates the artist's techniqueof leaving white gaps between regions that the artist does not want toblend, because the pigment propagation stage may treat the entire imagesurface as ‘wet’ and potentially blendable, which in watercolorpaintings is known as the wet-on-wet painting technique. The edgedetection map 19 may be created by the process disclosed in theApplicant's co-pending application Ser. No. 14/250,475 using adifference of Gaussians process, where two images are convolved withblurs of different radii and then subtracted, leaving information thatfalls between a range of spatial frequency values.

To create the pigment propagation buffer, which may be the same size asthe edge buffer, the scaled down and lightened image 15 made from thesource image 11 from above may be utilized. An image segmentationalgorithm is run on the sealed and lightened source image 15, which mayoperate to create regions of similar color. The herein disclosed processpreferably deposits pigments in stages, using the pigment buffer, tosimulate an artist's painting process. Segmented regions are used tocreate clusters of colors that will eventually be copied to the pigmentbuffer over time.

The image segmentation algorithm may be a graph-based segmentationalgorithm. The algorithm may be as described in “Efficient Graph-BasedImage Segmentation” by Pedro F. Felzenszwalb, the disclosures of whichare incorporated herein by reference. Various artistic effects can beachieved with different segmentation algorithms. For example, the imagesegmentation algorithm utilized herein may allow for a ‘minimumsegmented region size’ so that the image may be further simplified(e.g., discarding regions below the minimum size). Alternatively, thesegmentation algorithm used may not require a ‘min segmented regionsize’ because the desired effect is for more detail in the paintedimage. The algorithm utilized herein may also permit specifying the‘color similarity’ required for forming of the regions (e.g., thealgorithm may form a plurality of color regions that have certainthreshold boundaries, within which the color, and potentially the size,of a scanned portion of the image must fail for it to be grouped withinone of those regions).

Also, a watershed segmentation algorithm may alternatively be usedinstead of an image segmentation algorithm. Additionally, segmentationcan of course be created by hand, similar to the way an artist generallycolorizes regions.

Thereafter, the color regions are sorted by color value (lightest todarkest), which will become the order by which they will be deposited bythe algorithm into the pigment buffer, and will subsequently be utilizedthereafter, because when painting wet-on-wet, artists will generallystart with the lightest colors and end with the darkest. This preventsdark areas of paint from bleeding for too long, which may ruin lighterareas of the painting that are supposed to remain light.

The edge detection map 19 from the previous step is also incorporatedinto the pigment buffer, to ensure that no pigment is placed near edgesthat have been deemed to be cleanly delineated. The edge areas in themap are used to remove color from the pigment buffer (i.e., colorswithin the edge areas are replaced with white, and when the colors aresorted, the white colors are the first added to the painting, but theeffect is ‘null’ because it is the lightest color).

Next, the pigment propagation stage can begin. The pigment propagationstage operates to deposit each of the regions of color that weredetected by the image segmentation algorithm. The pigment propagationstage deposits the colors in multiple passes, depositing only one colorat a time, in each of the passes, using the detected colors and theregion boundaries that were sequentially stored in the pigment buffer.The simulation uses a diffusion of water technique that emulateswet-on-wet watercoloring. So, the pigment propagation stage operates todeposit the regions of color, with a darkening only color diffusion,with the order of color deposition going from the lightest colors to thedarkest colors (i.e., the color value order of the pigment propagationbuffer), while nonetheless enforcing each of the strict edge boundariesin accordance with the edge map. Since the pigment propagation stageoperates with a darkening-only methodology, the darker colors overwritethe white areas.

The pigment propagation stage operates analogously to a prior artbilateral filter, an example of which is shown in FIG. 4, operatingtherein on a single channel grayscale image, which produces thebilateral blurred image. Implementations of this type of filter can bevery simple, e.g., a 3×3 cross filter applied repeatedly to the sourceimage, and with the intensity controlled by repeated application of thefilter, with the output of each pass being used as the input to the nextpass.

However, watercolor simulation produced by the pigment propagation stageherein adds a unique twist: the output buffer of the bilateral filter isnot based on values read from the input buffer. Instead, two separatelymaintained buffers of identical size are used—the Edge Buffer and aPigment Buffer.

The Edge Buffer is utilized and is never altered, it is maintains aread-only status throughout subsequent executions of the filter.

The color values of the Pigment Buffer are read as input and written asoutput, based on corresponding pixels in the Edge Buffer. For eachpixel, the bilateral filter calculates the contribution of its adjacentneighbor pixels, then uses these values to read a fraction of theadjacent neighbor pixels from the Pigment Buffer and computes the finalpixel value as an average of its weighted neighbors. (See e.g., “PixelAveraging Smooth Graphics Effects,” by David Cook, the disclosures ofwhich are incorporated herein by reference). However, the final pixelvalues are written using a mint) test that only changes the pixel valueif the computed value is darker than the previous value at that pixel.

The Pigment Buffer starts out with each pixel at maximum value andpigment values are written to the Pigment Buffer before the simulationbegins. This results in darker values spreading across the PigmentBuffer. When the Pigment Buffer is composed of 3 RGB channels it givesthe appearance of color blending. (The method is simulating thesubtractive color model of real pigments using an RGB (additive colormodel) buffer by using the mathematical Min( ) function duringiterations of the within the pigment propagation stage(s) to make theoutput pigment buffer grow progressively darker by only writing valuesthat are darker than what was there previously).

Therefore, the pigment propagation stage runs a simple cross filterrepeated on the Pigment Buffer, spreading darker values during eachpass. This filter is designed to be implemented on a parallel system,with its implementation using an OpenGL fragment shader to run each passin parallel, hundreds of times.

As seen in FIG. 6 for the iterative steps 23, 25, 27, and 29, theseframes show aggregate steps of color deposition. For computationalefficiently, the depositing of color may be batched and a bunch ofcolors may be deposited in one step, e.g., depositing the first 50lightest color regions, then the next 50 regions, etc. With eithermethod of deposition (i.e., individual color deposition or batchdeposition), the simulation may progress at a desired rate to produce adesired visual effect: the user “sees the image being painted” in frontof them ( on screen) and can watch the painting progress and theprogression of the color bleeding effects, which users may findvisually-interesting.

The output image 29 of pigment propagation stage is then sent throughseveral compositing stages, which may add watercolor sedimentation(e.g., using a map consisting of mainly low-frequency noise) andflocculation textures (e.g., using a map consisting of mainlyhigh-frequency noise), which may be created by scanning real watercolorsurfaces and/or generated with synthetic noise algorithms, and alphablending them therewith. (Note, alpha blending is a process thatcombines an image with a background to communicate the transparency of asurface). The scanned watercolor images used for the maps may be largeareas of watercolor paintings that were particularly painted as evenlyas possible, and were then used for creating a repeating pattern of thetexture. Color is removed to create a single channel image that iscombined with the output pigment buffer to take on the colors from thepigment output buffer. A library of differentpaper/sedimentation/flocculation textures is created to simulatedifferent paper effects.

Additionally, a paper texture pattern may be composited therewith, toproduce the final image 31.

Also, a drawing layer may be composited therewith, which drawing layermay be in accordance with the “detail bandpass map” and “post-processfor detail reduction” step of the Applicant's co-pending applicationSer. No. 14/250,475. The drawing layer may then further post-processed,to simulate pencil, pen, etc.

Software of the present invention may ran on a suitable computingdevice, such as a server, a tablet, a cell phone, or other mobile smartdevice, so a description of such an accessorized exemplary computersystem is hereinafter disclosed, even though a particular embodiment maynot require the described components. Exemplary computer system 200(i.e., a client device associated with a particular user) is shownschematically in FIG. 7, and which may comprise computing unit 201 thatmay interact with external peripherals 202, such as a separate touchscreen display 244, and may interact with network resources 203,including use of the internet 261, and other computers (or other clientdevices or a server), which may be a laptop computer 262 (i.e., a secondclient device associated with a second user), a smart phone 263 (i.e., athird client device associated with a third user), a server 264, etc.

The computing unit 201 may include a data bus 224 for communicatinginformation across and among various parts of computing unit 201, and acentral processing unit, which may be a microprocessor (hereinafter“processor” or “CPU”) 222 coupled with a bus 224 for processinginformation and performing other computational and control tasks.Computing unit 201 may also include a volatile storage 225, such as arandom access memory (RAM) or other dynamic storage device, coupled tobus 224 for storing various information as well as instructions to beexecuted by processor 222. The volatile storage 225 may also be used forstoring temporary variables or other intermediate information duringexecution of instructions by processor 222. Computing unit 201 mayfurther include a read only memory (ROM) or an erasable programmablememory (EPROM) 227 or other static storage device coupled to bus 224 forstoring static information and instructions for processor 222, such asbasic input-output system (BIOS), as well as various systemconfiguration parameters. A persistent storage device or non-volatilememory 226, such as a magnetic disk, optical disk, or solid-state flashmemory device may be provided and may be coupled to bus 224 for storinginformation and instructions.

Computing unit 201 may be coupled via bus 224 to an integral display221, possibly a touch-screen display, for use in displaying informationto a user. If desired, computing unit 201 may be coupled via bus 224 toan external display screen 244. An external input device 243 (e.g., astandard keyboard) may be coupled to bus 224 for communicatinginformation and command selections to processor 222. A cursor controldevice 242, such as a mouse, a trackball, or cursor direction keys, maybe used for communicating direction information and command selectionsto processor 222 and for controlling cursor movement on display 244. Anexternal storage device 241 may be connected to the computing unit 201via bus 224 to provide an extra or removable storage capacity for thecomputing unit 201, which may be used to facilitate exchange of datawith other computer systems.

Some of the techniques herein may be performed by computing unit 201 inresponse to processor 222 executing one or more sequences of one or moreinstructions contained in the volatile memory 225. Execution of thesequences of instructions contained in a non-transitory memory may causeprocessor 222 to perform the process steps described herein. Inalternative embodiments, specific hard-wired digital circuitry may beused in place of, or in combination with, software instructions toimplement the invention.

The term “computer-readable medium” as used herein refers to any mediumthat participates in providing instructions to processor 222 forexecution. The computer-readable medium is just one example of amachine-readable medium, which may carry instructions for implementingany of the methods and/or techniques described herein. Various forms ofcomputer readable media may contain one or more sequences of one or moreinstructions for the processor 222 to execute, including non-volatilemedia (storage device 226), and volatile media (storage device 225).Common forms of computer-readable media include, for example, a floppydisk, a hard disk, magnetic tape, or any other magnetic medium, aCD-ROM, a flash drive, and a memory card.

The computing unit 201 may thus also include a communication interface,such as network interface card 223 coupled to the data bus 222.Communication interface 223 may provide a two-way data communicationcoupling to a network link that may be connected to a local network. Forexample, communication interface 223 may be an integrated servicesdigital network (ISBN) card or a modem to provide a data communicationconnection to a corresponding type of telephone line, or it may be alocal area network interface card (LAN NIC) to provide a datacommunication connection to a compatible LAN.

Network link 223 also typically provides data communication to othernetwork resources. For example, the network link may provide aconnection over the internet 261 to the world-wide-web. Thus, thecomputing unit 201 can access resources located anywhere using theInternet 261. Also, the computing unit 201 may also be accessed by, orcommunicate with, other computers (e.g. 262), or another smart device(e.g., smartphone 263), generally with permission, and which may belocated anywhere with access to the internet 261.

While illustrative implementations of one or more embodiments of thepresent invention are provided hereinabove, those skilled in the art andhaving the benefit of the present disclosure will appreciate thatfurther embodiments may be implemented with various changes within thescope of the present invention. Other modifications, substitutions,omissions and changes may be made in the design, size, materials used orproportions, operating conditions, assembly sequence, or arrangement orpositioning of elements and members of the exemplary embodiments withoutdeparting from the spirit of this invention.

Accordingly, the breadth and scope of the present disclosure should notbe limited by any of the above-described example embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

I claim:
 1. A computer implemented method of simulating an artist'sredrawing technique for creating a simulated watercolor image from asource image, said method comprising: inputting the source image into acomputer system; adjusting one or more luminance values for lighteningof the inputted image for producing an adjusted image; converting theadjusted image to a modified image; using an edge detection map toproduce a control image; determining a set of colors used in the sourceimage; determining a color region where each of the colors of the set ofcolors appear, and storing color values and color regions; coloring inmultiple passes, in a diffusion of water technique emulating wet-on-wetwatercoloring; coloring each of the color values with a darkening onlycolor diffusion, by coloring in a light to dark order; adding jitterduring said coloring using a noise pattern; and using the control imagefor said coloring in each of said multiple passes to control a diffusiongeometry for each of the color regions.
 2. The method according to claim1 wherein said control image undergoes compositing to add sedimentationtexture.
 3. The method according to claim 1 wherein said control imageundergoes compositing to add flocculation texture.
 4. The methodaccording to claim 1 wherein said control image undergoes compositing toadd a drawing layer.
 5. The method according to claim 1 wherein saidmodified image is a single channel image.
 6. The method according toclaim 1 wherein said modified image is a grayscale image.
 7. A computerimplemented method of simulating an artist's redrawing technique forcreating a simulated watercolor image from a source image, said methodcomprising; inputting the source image into a computer system; adjustingone or more luminance values for lightening of the inputted image forproducing an adjusted image; converting the adjusted image to a modifiedimage; using an edge detection map to produce a control image;determining a set of colors used in the source image; determining acolor region where each of the colors of the set of colors appear, andstoring the color values and color regions; coloring in multiple passes,using the color values and color regions and adding jitter during saidcoloring using a noise pattern; coloring each of the color values bycoloring in a light to dark order; and using the control image for saidcoloring in each of said multiple passes to control a diffusion geometryfor each of the color regions.
 8. The method according to claim 7wherein said control image undergoes composting to add sedimentationtexture.
 9. The method according to claim 7 wherein said control imageundergoes compositing to add flocculation texture.
 10. The methodaccording to claim 7 wherein said control image undergoes compositing toadd a drawing layer.
 11. The method according to claim 7 wherein saidmodified image is a single channel image.
 12. The method according toclaim 7 wherein said modified image is a greyscale image.
 13. A computerimplemented method of simulating an artist's redrawing technique forcreating a simulated watercolor image from a source image, said methodcomprising: inputting the source image into a computer system; adjustingone or more luminance values for lightening of the inputted image forproducing an adjusted image; converting the adjusted image to an imagehaving one luminance value for the image per pixel; using an edgedetection map to produce a control image; determining a set of colorsused in the source image; determining a color region where each of thecolors of the set of colors appear in the control image, and storing thecolor values and color regions; coloring in multiple passes, using thecolor values and color regions in a diffusion of water techniqueemulating wet-on-wet watercoloring, and adding jitter during saidcoloring using a noise pattern; coloring each of the color values withthe darker colors traveling the shorter distance; and using the controlimage for said coloring in each of said multiple passes to control adiffusion geometry for each of the color regions.
 14. The methodaccording to claim 13 wherein said control image undergoes compositingto add sedimentation texture.
 15. The method according to claim 13wherein said control image undergoes composting to add flocculationtexture.
 16. The method according to claim 13 wherein said control imageundergoes compositing to add a drawing layer.
 17. The method accordingto claim 13 wherein said modified image is a single channel image. 18.The method according to claim 13 wherein said modified image is agreyscale image.